Protocol composition in practice in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is protocol composition in Swift?

Protocol composition lets you combine multiple protocols into one requirement, so a type must conform to all of them at once.

beginner

How do you write a protocol composition type in Swift?

Use the syntax: ProtocolA & ProtocolB to require a type that conforms to both ProtocolA and ProtocolB.

intermediate

Why use protocol composition instead of inheritance?

Protocol composition allows combining behaviors from multiple protocols without needing a class hierarchy, making code more flexible and reusable.

beginner

Example: What does this mean? <br>func performAction(on object: Drawable & Animatable)

The function requires an object that conforms to both Drawable and Animatable protocols, so it can draw and animate the object.

intermediate

Can protocol composition be used with class-only protocols?

Yes, you can combine class-only protocols using protocol composition, and the resulting type will also be class-constrained.

Which syntax correctly represents protocol composition in Swift?

A ProtocolA + ProtocolB

B ProtocolA | ProtocolB

C ProtocolA, ProtocolB

D ProtocolA & ProtocolB

Protocol composition uses the & symbol to combine protocols.

What does a function parameter typed as Readable & Writable require?

A An object that is both Readable and Writable

B An object that is only Readable

C An object that is neither Readable nor Writable

D An object that is either Readable or Writable

The & means the object must conform to both protocols.

Can protocol composition be used with structs in Swift?

A No, only classes can use protocol composition

B Only enums can use protocol composition

C Yes, any type can conform to multiple protocols

D Only protocols can use protocol composition

Structs can conform to multiple protocols and be used with protocol composition.

What is a benefit of using protocol composition?

A It allows combining multiple behaviors flexibly

B It forces inheritance from a single class

C It restricts types to only one protocol

D It replaces all protocols with classes

Protocol composition lets you combine multiple protocols for flexible design.

If a protocol is class-only, what happens when you compose it with another protocol?

A The composition is no longer class-only

B The composition remains class-only

C The composition becomes a struct

D The composition is invalid

Class-only constraints carry over in protocol composition.

Explain how protocol composition works in Swift and give a simple example.

Think about how you can require multiple behaviors at once.

Describe a real-life scenario where protocol composition would be useful in Swift programming.

Imagine an object that needs to do more than one thing.